Currently, to improve comfort for a user and meet requirements of human engineering, adjusting means have been widely employed in modern chairs to adjust height of armrest according to actual stature of the user.
For example, Taiwan issued patents M333118 and M269800 both disclose a typical armrest for a chair which employs an adjusting means. However, the structure of these armrests is complicated and the great number of parts leads to high complexity in assembling such adjusting means. Accordingly, the material cost and assembling cost are too high. Therefore, there is a desire to develop a new armrest for a chair to overcome above problems.